"Lord of Light" by Roger Zelazny (Science Fiction, spoilers)

This novel won the 1968 Hugo award for best novel. Actually, even though it is science fiction, it is heavily influenced by religion, and many religious ideas are fundamental to the setting.

But it's still science fiction, and actually takes place in a future on a world in which technology has made certain religious ideas possible to apply in a more direct, observable fashion. Minds can be transferred to new bodies, and a system of reincarnation is in place. Depending on the life you've led, you can be reincarnated into a lesser body or even an animal, or you can aspire to becoming a god and joining the gods in heaven. Heaven is an actual, physical place on this world, reachable only by air.

The main character in the novel goes by the name "Sam," although he has other names at different times and in different contexts. Sam has some ideas that go against tradition. On this world, technology is not used beyond a medieval level by ordinary people, although clearly some forms of advanced technology make the reincarnation process possible.

Sam wants to change this, wants to make it easier for people to attain godhood and for people to develop more advanced technology. This leads him into conflict with the gods.

The whole idea of religion and tradition in conflict with technology is nothing new. What Zelazny does here, though, is something we haven't always seen in science fiction. Much of science fiction fandom, and writers, aren't as big on discussing religion in depth as they are technology and science. This novel does a very neat job of combining these. Like the presence of demons in the story, which are really natives of the world, composed of energy. Sam imprisoned them a long time ago, as humans wanted to claim the world for their own. This description is something that would be plausible in a religious context, but has enough science fictional resonance to suit the genre.

The plot is very sophisticated, a lot happens, with a fairly large cast of characters. I won't try to discuss them all in depth here.

One thing that's neat about the ending is the fact that the "winners" only win victory at a severe price. In the long term, it might be the losers who ultimately win.

This isn't exactly what I'd call light, easy reading - Zelazny crams a lot of ideas and plot into a relatively short novel, so you have to pay close attention to what's going on and remember who all the characters are, even though they have exotic names and some of them go by more than one name, at least Sam does. This is more of a book that you should be prepared to work at to follow and appreciate, not something to read as a mere entertaining distraction.

Some neat ideas, though, and certainly different from a lot of the science fiction I've read.